This invention relates to a new and improved power steering valve and more specifically to a valve sleeve having internal grooves which are formed with a rotating cutting tool, such as an end mill.
Many known power steering arrangements have valves to control the flow of fluid to a hydraulic motor. These valves may include an inner valve member which is rotated relative to a valve sleeve against the influence of a biasing spring. Relative rotation between the inner valve member and the valve sleeve directs a flow of fluid to the power steering motor to effect turning movement of the vehicle wheels in a known manner. Various known power steering systems having valves which operate in this manner are disclosed in U.S. Pat. Nos. 3,022,772; 3,667,346; 3,896,702; and 3,921,669.
Difficulty has been encountered in forming axially extending grooves on the inside of the valve sleeve. This difficulty results from the fact that the inside of the hollow cylindrical valve sleeve is relatively inaccessible. In order to form the axially extending grooves on the inside of the valve sleeve, it has been suggested that both a cutting tool and the valve sleeve be oscillated relative to each other through a plurality of strokes in order to enable the cutting tool to gradually form a slot or groove in the valve sleeve in the manner disclosed in U.S. Pat. No. 3,591,139. However, it is believed that this method of forming the valve sleeve is less than completely satisfactory since the method is relatively slow and requires a relatively complicated arrangement to oscillate both the valve sleeve and the cutting tool. It has also been suggested that electrochemical machining processes or spark erosion processes could be utilized to form the grooves inside the valve sleeve in the manner disclosed in British Pat. No. 1,427,705. However, these processes are not entirely suitable for producing the precise fluid control surfaces required in control valves of this type.